Views: 888 Author: Yosun Publish Time: 2024-12-13 Origin: Site
The pulping and papermaking process requires a large amount of production water. The wastewater generated by bleaching agents, fillers, and their reaction products are all pulping and papermaking wastewater. The primary sources of wastewater are the cooking waste liquid produced during the pulping and cooking process, the mid-stage wastewater produced during the middle stages of the pulping process (washing, screening, bleaching, and beating), and the paper machine white water produced during the papermaking process.
During the cooking process, high-concentration waste liquor containing a variety of chemical substances will be produced: the cooking waste liquor produced by alkali pulping is called black liquor because it appears black, and the cooking waste liquor produced by the sulfite pulping method is called red liquor because it appears red. It's called red liquid. At present, most paper mills use the alkaline cooking pulping process. The main components of the black liquor produced are lignin, polypentose, and total alkali, and they contain high concentrations of BOD and COD.
If paper mills discharge substandard wastewater, they will pollute water sources, human health, and the environment, and directly harm human health and the living environment.
The harm of papermaking wastewater, on the whole, is first harm to water bodies, then to aquatic organisms, through the food chain, etc., and finally to the human body. If people drink contaminated water, it will directly harm their health. Pollutants ultimately affect the entire environmental system through energy conversion and material circulation.
1. High suspended solids content
Paper wastewater contains a large number of fine fibers, fillers and other solid particles, resulting in a high concentration of suspended matter.
2. High organic matter load
Including lignin, cellulose degradation products, hemicellulose, etc., making the wastewater chemical oxygen demand (COD) and biochemical oxygen demand (BOD) is high.
3. Deep color
Due to the use of various dyes and additives, the wastewater usually has a dark color.
Second, the working principle and advantages of dissolved air flotation machine
The working principle of dissolved air flotation machine is to make air dissolved in water under a certain pressure to form dissolved air water, and then release a large number of tiny bubbles under atmospheric pressure. These bubbles in the process of rising with the suspended solids, colloids and other pollutants in the wastewater adhesion, the formation of specific gravity is less than the water of the air flotation body, so that the pollutants float to the surface of the water, to achieve solid-liquid separation.
Its advantages are:
1. Highly efficient removal of suspended solids
It can effectively remove the fine fibers, fillers and other suspended matters in paper wastewater and improve the clarification of wastewater.
2. Reduce the content of organic matter
Part of the organic matter will be removed with the air flotation process, thus reducing the COD and BOD value of wastewater.
3. Small footprint
Compact equipment structure, suitable for paper mills with limited space.
As one of the critical components in the advanced treatment technology system of pulping and papermaking wastewater, adsorption treatment technology emphasizes the application of active groups on the adsorbent to selectively enrich some inorganic pollutants to achieve purification of pulping The purpose of papermaking wastewater.
Supported by current technical conditions, the adsorbents selected during the advanced treatment of pulping and papermaking wastewater include fly ash, activated carbon, activated coke, and diatomaceous earth, among which activated carbon is the most widely used. Compared with other types of adsorbents, activated carbon has a series of advantages, such as a large pore structure and large specific surface area, which is of great significance in promoting the formation of chemical bonds between the active groups on the surface of the adsorbent and the adsorbed substances. On this basis, pulp and paper wastewater pollutants are deeply removed through intermolecular attraction. However, with the accumulation of relevant practical experience, when applying activated carbon adsorption technology for advanced treatment of pulping and papermaking wastewater, special attention must be paid to operating and regeneration costs. The cost is relatively high. How can we achieve this without affecting the treatment effect? Reasonably reducing costs is a topic that must be considered in the next stage of work.
In addition, activated coke is a commonly used adsorbent component. It is made from lignite. Its adsorption capacity is equivalent to activated carbon, with lower cost and poor pulverization. It has more specific application value for the advanced treatment of pulping and papermaking wastewater and deserves attention.
1. Efficient removal of suspended matter and organic matter
Dissolved air flotation can effectively remove suspended matter, grease, and other organic matter in papermaking wastewater, and the treatment efficiency can usually reach more than 90%.
2. Strong adaptability
The water quality of papermaking wastewater varies greatly. The dissolved air flotation system can adjust the operating parameters according to different water qualities to maintain a good treatment effect.
3. Small footprint
Compared with traditional treatment systems such as sedimentation tanks, the dissolved air flotation equipment has a relatively small footprint and is suitable for factories or treatment sites with limited space.
4. Easy operation
The operation and maintenance of the dissolved air flotation system are relatively simple, and it can achieve automatic control and reduce manual intervention.
5. Energy saving and environmental protection
Using dissolved air as buoyancy can effectively reduce dependence on chemical agents and is relatively environmentally friendly during flotation.
6. Effective color removal
Some papermaking wastewater may have color. Dissolved air flotation technology can remove pigments in sewage to a certain extent, thereby improving the appearance of sewage.
7. Reduce the subsequent treatment load
After removing the suspended solids and grease in the wastewater through pretreatment, the efficiency of subsequent biological treatment or other treatment processes can be effectively improved, and the treatment cost can be reduced.
8. Can be used in conjunction with other processes
Dissolved air flotation can be combined with sedimentation, filtration, biological treatment, and other processes to form a comprehensive treatment plan that improves the overall sewage treatment effect.
